Add key and value into StringDictionary in C#

The StringDictionary class in C# provides a specialized collection for storing string key-value pairs. It is case-insensitive, meaning keys are automatically converted to lowercase when added. The Add() method is used to insert new key-value pairs into the collection.

Syntax

Following is the syntax for adding key-value pairs to a StringDictionary −

StringDictionary dictionary = new StringDictionary();
dictionary.Add(key, value);

Parameters

• key − The key to add to the StringDictionary (string type).

• value − The value associated with the key (string type).

Key Rules

• All keys are automatically converted to lowercase when added.

• Keys must be unique − adding a duplicate key throws an exception.

• Both keys and values must be strings.

• The collection is case-insensitive for key lookups.

Using Add() Method

Example

using System;
using System.Collections;
using System.Collections.Specialized;

public class Demo {
   public static void Main() {
      StringDictionary strDict = new StringDictionary();
      strDict.Add("A", "John");
      strDict.Add("B", "Andy");
      strDict.Add("C", "Tim");
      strDict.Add("D", "Ryan");
      strDict.Add("E", "Kevin");
      strDict.Add("F", "Katie");
      strDict.Add("G", "Brad");
      Console.WriteLine("StringDictionary elements...");
      foreach(DictionaryEntry de in strDict) {
         Console.WriteLine(de.Key + " " + de.Value);
      }
   }
}

The output of the above code is −

StringDictionary elements...
a John
b Andy
c Tim
d Ryan
e Kevin
f Katie
g Brad

Adding Numeric String Keys

Example

using System;
using System.Collections;
using System.Collections.Specialized;

public class Demo {
   public static void Main() {
      StringDictionary strDict = new StringDictionary();
      strDict.Add("1", "Electric Cars");
      strDict.Add("2", "SUV");
      strDict.Add("3", "AUV");
      Console.WriteLine("StringDictionary elements...");
      foreach(DictionaryEntry de in strDict) {
         Console.WriteLine(de.Key + " " + de.Value);
      }
   }
}

The output of the above code is −

StringDictionary elements...
1 Electric Cars
2 SUV
3 AUV

Checking for Existing Keys

Example

using System;
using System.Collections.Specialized;

public class Demo {
   public static void Main() {
      StringDictionary strDict = new StringDictionary();
      strDict.Add("Name", "Alice");
      strDict.Add("Age", "25");
      
      // Check if key exists before adding
      if (!strDict.ContainsKey("City")) {
         strDict.Add("City", "New York");
         Console.WriteLine("City added successfully");
      }
      
      // This will check for lowercase key
      Console.WriteLine("Contains 'name': " + strDict.ContainsKey("name"));
      Console.WriteLine("Contains 'NAME': " + strDict.ContainsKey("NAME"));
      
      Console.WriteLine("Count: " + strDict.Count);
   }
}

The output of the above code is −

City added successfully
Contains 'name': True
Contains 'NAME': True
Count: 3

Conclusion

The Add() method in StringDictionary allows you to insert string key-value pairs into a case-insensitive collection. Remember that all keys are automatically converted to lowercase, and duplicate keys will cause an exception to be thrown.